1. Technical Field
This invention relates in general to devices and methods for inspection and repair of piping, such as fluid distribution means, and in particular, to devices and methods for inspecting gas mains without interrupting gas service during the testing operation.
2. Description of the Prior Art
The transportation of natural gas, water, petroleum products, and other gases and fluids typically involves the use of pipelines, often of considerable lengths. Cross-country pipelines are, of course, of large diameters such as 12 inches, 24 inches and 30 inches in capacity. Such pipeline sizes are usually associated with the transporting of natural gas, and large sizes of pipes are normally fabricated of steel. In urban areas distribution of natural gas, and the distribution of manufactured gas in previous years, is accomplished through vast networks of smaller size buried pipe, principally of four inch and six inch diameters. While present installation of underground pipe utilizes steel, particularly for natural gas of the four inch and six inch diameter size, thousands of miles of cast iron pipe have been installed and buried over the years, and are presently in use for the delivery of natural gas. In most of the United States cast iron gas distribution lines are often of four inches in diameter and typically include many 90 degree corners. Common problems encountered with buried cast iron pipe include deflection of the pipe caused by settling of the earth around the pipe, heaving due to frost (or forces applied to the earth around the pipe) causing cracking of the line and, often, the collection of water therein.
While numerous devices exist for the visual or other inspection of the interior of a pipeline, most, if not all, existing techniques have disadvantages which make their use at best inconvenient and, in all likelihood, difficult, time consuming and/or expensive. Many in-line pipe inspection devices and methods require, for example, in the case of gas pipe lines, discontinuance of service and/or severing of the main for insertion of the inspection device from an open end of the main, which is a complicated and costly process involving bypass and stop-off procedures. Obviously, this technique is expensive both in terms of the interruption to the gas service and the damage caused to the gas main. Inspection devices so inserted may include a fixed centralizer feature for maintaining the in-line viewing assembly substantially concentric with the axis of the pipe.
There exists a genuine need in the field for a more practical, efficient and effective system and method for viewing the interior of a pipe, and particularly, a four inch or six inch diameter gas distribution pipe.